1. Field of the Invention
This invention relates to electromagnetic valves and, more particularly, to an electrohydraulic signal converter.
2. Description of the Prior Art
U.S. Pat. No. 4,682,629 discloses an electrohydraulic signal converter, also known as an electromagnetic proportional valve, which has an armature moving between two inlet channel orifices in a magnetic field generated by a pair of field coils. The armature is effectively connected to restrictors located at the inlet channel orifices and at least one drain passage is provided downstream of the restrictors. The signal converter produces a control or actuating pressure depending on an electrical signal applied to the field coils. The control pressure may be used to control either a distributing valve, a pump that can be swung out in both directions beyond a neutral position, a motor of a hydrostatic gear, or the like.
In this known converter, a pair of field coils are arranged in a common housing and, in response to applied electrical signals, act upon the armature located within the coils and between two restrictors that are integrated in associated inlet channel orifices. As dictated by the direction of armature movement, the orifice cross-section of the restrictor in the direction of movement is reduced by the front end of the armature. This reduces the discharging oil volume as well as causes the pressure in the associated inlet channel to rise. The pressure differential between the two inlet channels can then be used for the control purposes discussed above.
This known signal converter has a disadvantage in that even when it is not actuated, there is a constant flow of hydraulic oil from both inlet channels through the discharge channel. In addition, the volume of the constant discharging oil stream must be relatively large so that when the signal converter is actuated, a high control pressure can be produced in one of the inlet channels within a short time period.
It is an object of the present invention to provide an electrohydraulic signal converter which has a reduced flow of discharging hydraulic oil.